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Human cloning is one of the most revolutionary yet controversial topics in the world of genetic research. To clone, or create an organism with an exact genetic copy as that of an existing organism’s, not only provokes a plethora of ethical concerns but further surfaces an exuberant amount of challenges and genetic risks to safely and successfully carry out such a process. This complex issue was brought to surface in the study, “Bringing Back Baby Jason” by Jennifer Hayes-Klosteridis. In this case study, the McMaster family is compelled to decide whether or not they should clone their recently deceased Baby Jason, in their last hopes of ever “bringing him back” and also their final chance for ever having biological children. To do so, scientists would have to carry out Somatic Cell Nuclear Transfer (SCNT), the most current and established practice for the reproductive cloning of mammals. In SCNT, the nucleus of an unfertilized egg is removed and replaced by the nucleus of a somatic cell, such as Baby Jason’s skin cell, upon which an electric shock would stimulate the mitotic cell divisions. If successful, the new child would present as an exact genetic match to his brother Baby Jason. Yet, from physiological and psychological risks, to tremendous genetic and epigenetic challenges, there are numerous factors the family and scientists have to consider before approaching the process of successfully cloning Baby Jason.
A number of epigenetic barriers and the extremely low success rate of producing a viable embryo are just two of the many challenges to cloning Baby Jason. Firstly, if human cloning could occur, the most likely approach method would be through SCNT, in efforts to ultimately produce a blastocyst, an early stage embryo. This process as a whole however presents an extremely low success rate, primarily due to epigenetic barriers. Epigenetics, the study of heritable differences in gene expression that does not involve changes to the underlying DNA sequence, is a primary source of many of the risks to producing a viable clone. Since the donor nucleus would come from Baby Jason’s skin cell, a differentiated cell, it would already contain preexisting epigenetic tags. While these tags control gene regulation and cell performance, the new egg cell drastically attempts to erase them through a process that is often delayed and/or incomplete, thereby resulting in an unviable embryo. These challenges and the low success rate of producing a viable clone are best evident through data from the renowned cloning of Dolly the Sheep.1 According to the Roslin Institute, out of the 277 eggs used via SCNT, 29 viable embryos were produced, only 3 survived till birth, and only one sheep made it to adulthood, Dolly.1 The relatively low success rate for producing a viable embryo due to one’s epigenome proposes tremendous challenges for successfully cloning Baby Jason.
Among the other challenges, genomic imprinting would posses numerous problems for the successful cloning of Baby Jason. Genomic Imprinting is essentially the idea that whether or not a given gene is expressed in the offspring ultimately depends on which parent, mother or father, the gene was inherited from. In diploid organisms, imprinting ultimately results in one of the two alleles being silenced. Since the genes that undergo imprinting are ‘marked’(via methylation) during the formation of egg and sperm cells, scientists can identify if the copy of the gene was inherited from the mother or the father. Challenges would arise however, as the tags on Baby Jason’s skin cell nucleus had been copied over several times. Despite the highly reliable process of DNA copying, the process of copying epigenetic tags depicts a much greater error rate. DNA code copying for example results in one error per half a billion, while epigenetic copying can result in error rates as high as one in twenty-five.1 Even a few resulting miscopied epigenetic tags could have tremendous and terrible consequences in the development and survival of Baby Jason’s clone.
Chromatin modifications and the parts of a chromosome would both play a tremendous role in the production of a viable and healthy clone of Baby Jason. Firstly, chromatin modifications consist of DNA methylation and histone modification, including (acetylation, phosphorylation, methylation, etc.), and they ultimately serve to make chromosomal DNA more or less accessible to transcription. For starters, DNA methylation is an epigenetic mechanism that involves the addition of a methyl group to a DNA base, while also playing a role in the expression of retroviral genes and the suppression of harmful DNA sequences. Histone modifications, on the other hand, affect gene expression by altering the chromatin structure. Histone methylation for example, regulates gene expression and ultimately affects many biological outcomes such as longevity, DNA repair, transcription, among others. Both these forms of chromatin modification would greatly affect the cloning of Baby Jason, as they are cumulatively responsible for controlling the activation of transcription, chromosome packaging, and DNA repair, all crucial processes to the survival and proper development of the newly cloned child. Additionally, the various parts of a chromosome would also influence the viability and survival of the newly cloned child. For example, telomeres, the protective ends on the tips of eukaryotic chromosomes, play a crucial role in determining the longevity of an organism. Since cells contain little telomerase, every time DNA replicates, the telomeres get shorter, ultimately causing the cell to stop dividing as the cell ages. Consequently, this can impact human cloning, as the donor nucleus comes from an older human being (with shorter telomeres), thereby resulting in possible premature ageing within the cloned child. Baby Jason was two years old when he died however, so the impact of his slightly shortened telomeres may not be as drastic on his cloned brother, as they were for Dolly the Sheep’s 6 year old donor1.
Due to the tremendous genetic and epigenetic challenges, in addition to physiological and psychological risks, the McMasters’ family should not clone their Baby Jason. From genomic imprinting and epigenetic markers to chromatin modifications, there are a tremendous amount of challenges to producing a viable and healthy child. Even if the cloned child survived post partum, he would not “replace” Baby Jason, as the environments they grow up in and the people they meet will influence both boys in a different manner entirely. This is simply due to the fact that our entity as a whole is shaped by our surrounding environment (nurture), and our genetic makeup (nature). On the whole, the McMasters’ should not clone their Baby Jason due to the overwhelming biological risks associated with such a novel process.
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